C++: Handle C++ style comments in macro expansion

Notice that a similar problem still exists for which we
need to fix the lexer when there's a C style commend which
 ends with a backslash-newline.

Task-number: QTCREATORBUG-7713

Change-Id: I0f6d561703984f917fa5ed29de020ad0bdc5aaf0
Reviewed-by: David Schulz <david.schulz@nokia.com>
Reviewed-by: hjk <qthjk@ovi.com>

src/libs/cplusplus/pp-engine.cpp

@@ -1349,7 +1349,21 @@ void Preprocessor::scanActualArgument(PPToken *tk, QVector<PPToken> *tokens)
             break;
         }
 
-        tokens->append(*tk);
+        if (m_keepComments
+                && (tk->is(T_CPP_COMMENT) || tk->is(T_CPP_DOXY_COMMENT))) {
+            // Even in keep comments mode, we cannot preserve C++ style comments inside the
+            // expansion. We stick with GCC's approach which is to replace them by C style
+            // comments (currently clang just gets rid of them) and transform internals */
+            // into *|.
+            QByteArray text = m_state.m_source.mid(tk->begin() + 2, tk->end() - tk->begin() - 2);
+            const QByteArray &comment = "/*" + text.replace("*/", "*|") + "*/";
+            tokens->append(generateToken(T_COMMENT,
+                                         comment.constData(), comment.size(),
+                                         tk->lineno, false));
+        } else {
+            tokens->append(*tk);
+        }
+
         lex(tk);
     }
 }